The effectiveness of most Indoor Air Quality (IAQ) devices is heavily dependent on the volume of conditioned air that is passed through them. However, an issue arises when dehumidification is needed in the same conditioned space.
Air processing systems including a thermostat and a two-speed compressor are well known. The compressor may be part of a conventional air conditioner or heat pump. The compressor is cycled ON and OFF and between a LOW and HIGH speed in accordance with the temperature of the enclosed space and the thermostatic demand signals. HIGH cooling speed operation typically results when the enclosure temperature exceeds the set temperature of the thermostat by an incremental temperature, such as 2° F.
Processed air is delivered to the enclosed space by a blower. With a heat pump, the blower typically has two speeds and operates at HIGH speed during cooling and LOW speed during heating, regardless of compressor speed.
The cooling mode humidity controls incorporated into these types of air processing systems are electromechanical monitors designed solely to control blower speed. Whenever relative humidity of the enclosed space exceeds the set point of an electromechanical humidistat, the LOW blower speed is maintained. Slower air movement increases dehumidification in the area of the “cold” inside compressor coil.
However, these electromechanical humidity monitors are inefficient and inexact. While humidity reduction is generally enhanced, the temperature of the enclosed space is often not preserved, leading to higher energy costs. Additionally, the relative humidity tolerance of such monitors is much too great to provide adequate control for proper comfort.